The purpose of this study is to develop a new type of coated wire electrode for fine wire EDM. Piano wire with a very high tensile strength is coated with an electrically conductive brass layer to achieve high-speed and high-precision wire EDM. In our previous papers, using a thin wire of 50μm diameter, the thickness and quality of the brass coating layer were optimized and the effects of the tensile strength of the piano wire used as the core wire on machining characteristics were discussed. In this paper, the effect of surface roughness of the brass wire electrode was experimentally investigated. As a result, it was found that by using wire with relatively large surface roughness, the machining rate increased because of the high discharge frequency. Also, a more uniform distribution of the discharge location was confirmed by high-speed observation of the working gap during the process. In addition, the electrostatic field in the gap between the wire electrode and workpiece surface was analyzed and the reason for the high machining rate in case of the wire with relatively large surface roughness was discussed from the viewpoint of the distribution of electric intensity distribution on the wire surface.
A three-dimensional finite element model has been developed to simulate dynamically the laser micro-welding process of thin stainless steel sheet. The model can calculate the temperature distribution and predict the weld bead geometry during the welding process. The numerical simulation was conducted using a non-linear transient thermal analysis with changing the laser processing parameters; namely laser power, scan velocity and spot diameter under a constant energy density. The measurement of weld bead geometry from the laser micro-welding experiments was used to validate the developed numerical model. The results show that there are good agreements with the weld bead geometry between the experimental observations and the finite element simulations.
Gas components of bubbles generated in electrical discharge machining (EDM) were analyzed using gas chromatography to understand the phenomena related to evaporation and dissociation of dielectric liquids caused by discharge. When EDM oil was used as the dielectric, more than 50% of the gas components was found to be hydrogen. The other gases included oxygen, nitrogen, and hydrocarbon gases such as methane, ethylene, and acetylene. With increasing discharge energy, the percentages of hydrogen and hydrocarbon gases with smaller molecular weight increased due to the dissociation of the dielectric molecules. On the other hand, when deionized water was used as the dielectric, which is normally used in wire EDM, bubbles were composed of hydrogen, oxygen, and nitrogen. The ratio of oxygen to hydrogen was smaller than the ratio determined by stoichiometry due to oxidation in the gap. In the presence of equivalent discharge energy, the volume of bubbles generated in wire EDM using deionized water was significantly smaller than that in sinking EDM using oil. This is because hydrogen and oxygen generated due to dissociation in the discharge plasma recombine and condense to water after discharge.
A surface replication process is necessary for the mass production of nanometer-sized patterned and/or nanometer-flat surfaces. We have been developing a surface replication technique, aiming for 1 nanometer level replication accuracy in height direction. The process is based on nickel electroforming under low-temperature conditions. To investigate replication accuracy, we used an EEM (elastic emission machining) processed surface, having 0.1 nm flatness in root-mean-square (RMS) as a master surface, and compared the roughness of the master and replicated surfaces. The surface roughness is evaluated by using phase-shift microscopic interferometry and atomic force microscopy. The results indicate that surface replication is possible for one-nanometer.level smoothness. The durability of the master surface and repeatability of the process are also investigated. Surface quality of the master surface was found to be maintained during multiple electroforming processes.
Electrical discharge machined surface using the silicon (Si) electrode has excellent corrosion resistance because of the formation of an amorphous layer. In this study, Si-containing amorphous layer which was comparatively thick (about 10 μ m) was formed by electrical discharge coating, and the characteristics of this layer were investigated. Detailed metallographic analyses showed that the Si-containing amorphous layer had 7wt% of Si and the fine structures with crystalline existed in this layer. From the water jet test, it became clear that the Si-containing amorphous layer had excellent erosion resistance in addition to excellent corrosion resistance. Furthermore, the Si-containing amorphous layer had comparatively low friction coefficient and high wear resistance. The heating test showed that the Si-containing amorphous layer was kept amorphous in 500 degrees or less and that when the heating temperature exceeded 600 degrees, the layer crystallized so that the microcrystals of Fe3C and α-Fe were deposited.
This paper investigates the ease of bubble coalescence of the machining liquid and the medium at the discharge ignition location in electrical discharge machining (EDM) process in order to discuss the effect of the properties of the machining liquid on the material removal rate. Bubble coalescence, which is one of the properties of a machining liquid, was observed using a video camera, and the medium at the discharge ignition location, i.e., whether a discharge occurs in EDM oil or in bubbles, was determined using a characteristic of the waveform of the discharge current. It is found for a continuous EDM process that a high proportion of discharges occur near the boundaries of previously existing bubbles, whereas few discharges occur in the interior of bubbles. It is also found that reducing the bubble coalescence will improve the material removal rate.